Transport secretary Chris Grayling is preparing to delay the electrification of huge swathes of the railway network amid a deepening funding crisis at Network Rail.Plans to upgrade core stretches of track on the TransPennine, Midland Mainline and Great Western routes to run electric trains are set to be put back by years in favour of new “bi-mode” trains that run on both diesel and electricity.Instead, the state-owned Network Rail will be told to focus on its day job of maintaining and repairing existing tracks, amid growing concern that this has been neglected in favour of “trophy” electrification projects.